If you haven’t had your head in the proverbial sand of the fitness industry, you’ll know that kettlebells have gained a lot of popularity over the last decade. Although they have been used in Russia for several centuries, they have just recently caught on in the western fitness culture.

The kettlebell swing is one of the most popular exercises, and for good reason. As an exercise, it’s a primary activator of:

Obliques

Hip Flexors

Quadriceps

Gluts

And a secondary activator of:

Deltoids

Abdominal muscles

Erector spinae

Latissimus Dorsi

Hamstrings

In addition to being a great functional exercise, early research suggests it may help with neck, shoulder and back pain.

What the authors of this study wanted to know was which is a better way to work your core when doing this exercise as either a 1-armed or 2-armed swing.

Methods

They included 16 healthy men (roughly 25 years of age, and weighing approximately 175 lbs (80 kg); all with an average of 7 years of resistance training experience volunteered for the study.

The 1-armed and 2-armed kettlebell swing exercises were performed in a randomized and counterbalanced order.

They used Electromyelography or EMG electrodes placed on the underlying muscle fiber of the lower and upper erector spinae, rectus abdominis, and external oblique to measure their activity.

Results

For the upper erector spinae, the activation of the contralateral side (meaning the opposite side of the kettlebell) during 1-armed swing was 24% greater than that of the ipsilateral side (meaning the same side) during 1-armed swing (p , 0.001) and 11% greater during 2-armed swing (p = 0.026).

Furthermore, the activation in 2-armed swing was 12–16% greater than for the ipsilateral side in 1-armed swing (p , 0.001).

For the rectus abdominis muscles, however, 42% lower activation of the contralateral side was observed during 1-armed swing compared with ipsilateral sides during 2-armed swing (p = 0.038) and 48% compared with the ipsilateral side during 1-armed swing (p = 0.044).

Comparing the different phases of the swing, most differences in the upper erector spinae were found in the lower parts of the movement, whereas for the rectus abdominis, the differences were found during the hip extension.

For the lower erector spinae and external oblique muscles, there were no differences noted between the 1-armed and 2-armed swings (p = 0.055–0.969).

Conclusions

In conclusion, performing the kettlebell swing with 1 arm resulted in greater muscle activation for the contralateral side of the upper erector spinae and ipsilateral side of the rectus abdominis, and lower activation of the opposite side of the respective muscles.

My interpretation is that these results suggest that the 1-armed swing provides more muscle activation than the 2-armed swing for upper erector spinae and rectus abdominis muscles, but are equivalent for lower erector spinae and oblique muscles.

This argues, to me at least, that you should be doing 1 arm kettlebell swings for core exercise while recognizing that you need to do an equal number of sets and reps on each side.